As described in U.S. patent application Ser. No. 13/473,132 filed May 16, 2012 incorporated herein by reference, it is desirable to provide a thin structure for an antenna embedded in an armor panel and more particularly to provide a parasitic element, on top of the armor layer so that when driving the antenna there are no apertures in the armor which would degrade performance. In one embodiment the aperture-less embedded antenna system includes a direct fed dipole on the underneath side of the armor layer such that the armor layer is not pierced. There is an identical dipole on the top of the armor layer that is parasitically fed by the driven dipole. In one embodiment the dipoles are in the form of bowties.
As described in the above-identified patent application, it is desirable to replace antennas such as whip antennas on tanks, armored vehicles and the like with broadband antennas that are conformal to the vehicle itself.
Having a forest of antennas that extend from the armored vehicle is undesirable because they are susceptible to damage and attack. It is therefore desirable to be able to provide an antenna system which is embedded in the armor such that the armor protects the embedded antenna both against explosive attacks and ballistic penetration while at the same time eliminating the need for antenna whips, and the like which are easily blown off with explosive charges, thereby precluding communication with the vehicle.
It is noted that the thin structure of present armor panels presents the greatest challenge to antenna design. Whether the panel is metal backed itself or is mounted on a metal vehicle, the close proximity of a conductive surface to a radiating element creates a ground plane that is too close to the element. As will be appreciated in traditional antenna design, the ground plane is spaced at least a quarter wavelength away from any driven element. However, when dealing with armor for vehicles such as tanks and the like, the spacing between the ground plane and the driven element of the antenna is on the order of hundredths of a wavelength.
While initially thought that this limitation would be a disqualifying factor in the antenna design, it has been shown that a thin antenna structure can be created which does not rely on deep cavities behind the elements. However, it has been found that the close spacing described in the above patent application as well as other factors limits bandwidth and gain and results in non-optimal VSWR across the desired bandwidth for instance between 225 GHz and 450 GHz.
Note, deep cavity structures have been described in U.S. Pat. No. 6,833,815 which relates to Cavity Embedded Meanderline Loaded Antennas. In this patent the antenna described is a conformal antenna which is cavity-backed.
In one embodiment of this Cavity Embedded Meanderline Antenna a bowtie dipole is utilized, with the distal ends of the dipole being coupled to surrounding metal utilizing a meanderline structure. The question becomes how one can better configure such dipole antenna into a thin structure for use with at armor plates.